(1) Field of the Invention
This invention relates to a process for producing a gel-coated seed.
(2) Description of the Related Art
In recent years, a seed such as what is called xe2x80x9cF1,xe2x80x9d having an excellent gene has been commercially available on the basis of advancement in biotechnology. By employing such a seed, productivity has been remarkably improved and highly valuable farm produce has been yielded, attracting a considerable attention as a core technology for a rebirth of Japanese agriculture.
On the other hand, since such seeds are expensive, the seeds are required to be sown at a prescribed position in a field without wasting them and to germinate, grow and harvest securely. To meet with these requirements, a gel-coated seed has been developed, on which the present inventors have studied and proposed several techniques.
As disclosed in, for example, Japanese Patent Application No. H6-152068, a gel-coated seed is produced according to the steps of: dipping seeds into a gel-forming solution such as a sodium alginate aqueous solution; gathering the solution together with the seeds; dropping them into a gelatinizing solution containing, for example, calcium ions to form a coating gel-layer around each seed; and adjusting hardness of the coating gel-layer in the following washing step.
However, this process is time-consuming and some skillfulness is required in order to form a gel-coated seed in such a manner that one grain of seed is securely packed in one gel capsule and various controls and complex machines are needed for mechanization, causing such a gel-coated seed expensive after all.
In particular, it has been difficult to take out seeds dipped in a viscous gel-forming solution and to control a size of the gel-coated seed and a thickness of the coating gel-layer, therefore, hardness of the coating gel-layer has not been uniform causing from ununiformity in the thickness of the coating gel-layer, resulting in bad handling upon sowing, plugging in a sowing machine upon sowing by machine and a difficulty in secure sowing grain by grain. Furthermore, since the thickness and hardness of the coating gel-layer are not uniform, a germination rate has been low and a germination time has not been uniform from seed to seed.
In order to decrease the ununiformity in hardness of the coating gel-layer, a time for hardening and a time for washing can be adjusted, however, it is not practical to adjust the time for hardening and washing in accordance with each thickness of coating gel-layer of each seed.
It is therefore an objective of the present invention to solve the above problem and to provide a process for producing a gel-coated seed, by which an excellent gel-coated seed having a uniform thickness and hardness of the coating gel-layer can be produced.
In order to attain the above objective, the present invention is to provide a process for producing a gel-coated seed, employing a gel-forming solution and a hardener for gelatinizing the gel-forming solution, characterized in that a seed is dipped into the gel-forming solution after the hardener adheres to the seed.
A gel-forming solution used in a process for producing a gel-coated seed according to the present invention easily forms an aqueous gel by a hardener. The aqueous gel is relatively soft so that the aqueous gel neither adversely affect the seed nor prevent a plumule and radicle from growing. The gel-forming solution is a solution such as sodium alginate aqueous solution, sodium polyacrylate aqueous solution and sodium carboxymethyl cellulose (hereinafter, CMC-Na) aqueous solution.
The hardener for gelatinizing the gel-forming solution is a substance containing ions of bivalent metal such as calcium and barium (when sodium alginate or sodium polyacrylate aqueous solution is used as the gel-forming solution) or a substance containing aluminum ions (when CMC-Na aqueous solution is used as the gel-forming solution), wherein the substance is a salt such as chloride (solid) and lactate (solid) or an aqueous solution of the salt.
In the present invention, it is necessary that a seed be dipped into the gel-forming solution after the hardener adheres to the seed. Otherwise, neither an excellent effect of the present invention can be obtained nor a formation of the gel-coated seed itself can be attained according to circumstances.
In the present invention, adhesion of the hardener to the seed is easily carried out by spraying water onto the seed followed by adding a solid hardener and mixing, or dipping the seed into a liquid hardener followed by removing an excess hardener using a sieve and the like.
The seeds on which the hardener adheres are successively thrown into the gel-forming solution under stirring to form a coating gel-layer around the seed, then the gel-coated seeds are taken out from the gel-forming solution followed by washing.
During formation of the coating gel-layer, the formed gel-coated seeds possibly adheres with each other, and when the seeds rise to the surface partially coming out from a liquid level of the gel-forming solution, the coating gel-layer is not formed on a portion of the seed above the liquid level. In these cases, a sowing by machine might be impossible or a problem such as a lowering of a germination rate is often caused. Consequently, during the formation of the coating gel-layer, the gel-forming solution has to be well stirred so as to prevent the above problems from occurring.
The thickness and hardness of the coating gel-layer depend upon a concentration of the gel-forming solution and an adhesion amount of the hardener, and when these conditions are fixed, the thickness and hardness are determined by a dipping time of the seed into the gel-forming solution, therefore, the dipping time has to be adjusted according to a requirement. Thus formed gel-coated seeds are taken out from the gel-forming solution and immediately washed using water so as to remove unhardened gel-forming solution adhering around each gel-coated seed.
According to the present invention, no complicated equipment is needed, a relatively large quantity of the gel-coated seeds can be produced through simple steps such as throwing, stirring and washing, enabling a production at low cost. Further, the produced gel-coated seed has a uniform thickness of the coating gel-layer and hardness, enabling an easy sowing, a uniform germination, therefore, a simultaneous harvest, a good production efficiency and an easy mechanization for the harvest.